Optimal Synergistic Extraction of Cr(VI) from Aqueous Acidic Media Using Alamine 300/Aliquat 336 and Di-n-octyl Amine/Tributyl Phosphate Mixed Reagents

Data for the extraction of chromium(VI) from aqueous sulfate solutions by Alamine 300/Aliquat 336 and di–n–octyl amine/tributyl phosphate (DOA/TBP) have been subjected to formulation of an optimization structure for an effective Cr(VI) separation based on the derivative variation method. Both experimentally and analytically defined optimum Cr(VI) removal efficiencies are ranging about 83–99%, 71–93%, and 60–73% for Alamine 300/Aliquat 336, DOA/TBP, and DOA, respectively. Modeling efforts based on mass-action law methodology and non-homogeneous differential approach have shown considerable success yielding a 10% mean error, and satisfies established limiting behavior of the physical event.     

Solvent extraction of hexavalent chromium with tetrabutyl ammonium bromide from aqueous solution

The extraction of hexavalent chromium (Cr) from aqueous solutions by tetrabutyl ammonium bromide (TBAB) salt in dichloromethane was investigated. The results indicated that the maximum extraction efficiency of Cr(VI) was at pH 1±0.1. The strippant 0.1 M sodium hydroxide, completely stripped Cr(VI) from the loaded solvent. The stripped solvent can be reused for extracting Cr(VI). After five extraction cycles, the dichloromethane showed no significant loss in volume and retains the same extracting ability. The solvent extraction method was applied for the removal and recovery of Cr(VI) from real chromeplating wastewater and found to be satisfactory.     

Three-liquid-phase extraction and separation of V(V) and Cr(VI) from acidic leach solutions of high-chromium vanadium–titanium magnetite

A new method by liquid–liquid–liquid three phase system, consisting of acidified primary amine N1923(abbreviated as A-N1923), poly(ethylene glycol)(PEG) and (NH_4)_2SO_4 aqueous solution, was suggested for the separation and simultaneous extraction of V(V) and Cr(VI) from the acidic leach solutions of highchromium vanadium–titanium magnetite. Experimental results indicated that V(V) and Cr(VI) could be selectively enriched into the A-N1923 organic top phase and PEG-rich middle phase, respectively, while Al(III)and other co-existing impurity ions, such as Si(IV), Fe(III), Ti(IV), Mg(II) and Ca(II) in acidic leach solutions,could be enriched in the(NH_4)_2SO_4 bottom aqueous phase. During the process for extraction and separation of V(V) and Cr(VI), almost all of impurity ions could be removed. The separation factors between V(V) and Cr(VI) could reach 630 and 908, respectively in the organic top phase and PEG middle phase, and yields of recovered V(V) and Cr(VI) in the top phase and middle phase respectively were all above 90%.Various effects including aqueous p H, A-N1923 concentration, PEG added amount and(NH_4)_2SO_4 concentration on three-phase partitioning of V(V) and Cr(VI) were discussed. It was found that the partition of Cr(VI) into the PEG-rich middle phase was driven by hydrophobic interaction, while extraction of V(V) by A-N1923 resulted of anion exchange between NO_3~- and H_2V_(10)O_(28)~(-4). Stripping of V(V) and Cr(VI) from the top organic phase and the middle PEG-rich phase were achieved by mixing respectively with NaNO_3 aqueous solutions and Na OH-((NH_4)_2SO_4 solutions. The present work highlights a new approach for the extraction and purification of V and Cr from the complex multi-metal co-existing acidic leach solutions of high-chromium vanadium–titanium magnetite.     

THERMODYNAMIC EQUILIBRIA OF THE EXTRACTION OF CHROMIUM(VI) WITH TRI-N-OCTYLPHOSPHINE OXIDE FROM AQUEOUS SOLUTIONS

ABSTRACT

The distribution of chromium( VI ) between aqueous solutions and the kerosene solutions of tri-n-octyl-phosphine oxide (TOPO) have been studied at 25 °C and pH 2-4, in which range the predominant forms of Cr(VI) are HCrO₄ and Cr₂O₇ ^2?. The extraction equilibrium is influenced by the total chromium(VI) concentration, aqueous pH value, and total extractant concentration. The thermodynamic equilibria among all species in the aqueous phase were used for the analysis of distribution data, and the activity coefficients of ionic species were estimated according to Debye-Hiickel or Bromley equation. By numerical method, the complexes of Cr(VI ) with TOPO formed in the organic phase were found to be H₂CrO₄ (TOPO) and H₂Cr₂O₇ (TOPO) ₃. The corresponding extraction constants were 2019 and 3.69× 10⁸, respectively.     

Separation of Cr(VI) from Water by Green Reduction Reaction and Adsorptive Removal on Gelatin-Grafted-Yeast Biosorbent

A green chemical method was explored and described for separation and extraction of the toxic hexavalent chromium from aqueous solutions and real water samples. A green reduction reaction for the transformation of toxic hexavalent chromium into the nontoxic trivalent chromium ion was performed by using hydrogen peroxide. The produced Cr(III) was then extracted by biosorption on the surface of a novel and eco-friendly gelatin-grafted-baker’s yeast (Gelatin-Yeast) biosorbent. The investigated biosorbent was characterized by high capacity value of the reduced trivalent chromium species in pH 6.0 as 1.120 mmol g^?1. The biosorption processes were examined, monitored, and optimized in different experimental and controlling parameters. The potential applications of Gelatin-Yeast for separation and removal of Cr(VI) from real industrial and sea water samples were also studied.     

Removal of Cr(VI) from wastewater by adsorption on iron nanoparticles

Due to rapid industrialisation, the presence of heavy metals in water and wastewater is a matter of environmental concern. Though some of the metals are essential for our system but if present beyond their threshold limit value (TLV), they are harmful and their treatment prior to disposal becomes inevitable. The present communication has been addressed to the removal of Cr(VI) from aqueous solutions by nanoparticles of iron. Nanoparticles of iron were prepared by sol–gel method. The characterisation of the nanoparticles was carried out by XRD and TEM analysis. Batch experiments were adopted for the adsorption of Cr(VI) from its solutions. The effect of different important parameters such as contact time and initial concentration, pH, adsorbent dose, and temperature on removal of chromium was studied. The removal of chromium increased from 88. 5% to 99.05% by decreasing its initial concentration from 15 to 5 mg L^?1 at optimum conditions. Removal of Cr(VI) was found to be highly pH dependent and a maximum removal (100%) was obtained at pH 2.0. The process of removal was governed by first and pseudo‐second‐order kinetic equations and their rate constants were determined. The process of removal was also governed by intraparticle diffusion. Values of the thermodynamic parameters viz. ΔG°, ΔH°, and ΔS° at different temperatures were determined. The data generated in this study can be used to design treatment plants for chromium rich industrial effluents. Adsorption results indicate that nanoiron particles can be effective for the removal of chromium from aqueous solutions.     

Application of nanometer size of polypyrrole as a suitable adsorbent for removal of Cr(VI)

The objective of this work was to investigate the sorption characteristics of polypyrrole (PPy) for the removal of Cr(VI) from aqueous solutions. The sorption process was carried out by a dynamic batch method in order to determine the optimum conditions. For a sorbent dose of 0.6 g in 100 mL of a Cr(VI) solution, at a contact time of 15 min and a pH of 3, a removal efficiency of 84.5% was achieved. The Morris–Weber and Lagergren equations, as well as a pseudo‐second‐order equation were examined to explore the kinetics of the removal process. In addition, the Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models were applied to estimate the capacity, intensity, and energy of the sorption process. It was found that increasing temperature showed a positive effect on the ion sorption efficiency. In summary, PPy was shown to be a suitable candidate for chromium(VI) ion removal from aqueous solutions at different concentrations. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers.     

A POSSIBLE USE OF PHOTO-REACTION IN LIQUID-LIQUID EXTRACTION OF SUBSTITUTION-INERT METAL COMPLEXES. EXTRACTION OF CHROMIUM(III) AND COBALT(III) COMPLEXES.

A liquid-liquid extraction of chromium(III) ion was achieved by a cooperative action of light (photoreduction) and conventional extractants on chromium(VI) species. The extraction of chromium spcies was studied by both molecular and atomic absorption spectrophotometry measurements. Trioctylphosphine oxide (TOPO) was the most effective among the extractants studied (TOPO, dibutylsulfoxide, tributyl phosphate, 2-ethyhexyl hydrogen 2-ethylhexylphosphonate, di (2,4,4-trimethylpentyl)-phosphinic acid). A back-extraction of chromium(III) species to aqueous solution was also promoted by photo-irradiation. The nature of the extraction system was studied under various operational conditions such as wavelength of illuminating light, coordinating ah ionic species in aqueous solution, and coexisting metal ions. A liquid- liquid (back-) extraction of some     

Selective extraction and concentration of chromium(VI) from acidic solutions containing various metal ions through emulsion liquid membranes using Amberlite LA-2

Chromium(VI) is a very harmful metal, highly toxic and carcinogenic in nature. Its separation from industrial effluents is of primordial importance. An extensive study on selective extraction and concentration of chromium(VI) from the acidic solutions containing various metal ions using an emulsion liquid membrane (ELM) technique is presented. The ELM consists of Amberlite LA-2 as an extractant, commercial kerosene as organic solvent, ECA 4360J as a surfactant and 0.5 M ammonium carbonate solution as stripping phase. The study has highlighted the importance and influence of membrane composition for maximizing the extraction of chromium(VI). For this reason, effects of various parameters such as chromium(VI) concentration in the acidic solution, mixing speed, type and concentration of stripping solution, type and acid concentration of the acidic solution, extractant and surfactant concentrations, phase ratio and treatment ratio were studied and optimum conditions were determined. The results showed that it is possible to extract 99% of chromium(VI) from the acidic solution containing Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) ions, at the optimum conditions.     

Simultaneous Removal of Nickel(II) and Chromium(VI) from Aqueous Solutions and Simulated Wastewaters by Foam Separation

The present investigation was carried out to study the feasibility of foam separation for simultaneous removal of two types of inorganic hazardous contaminants, nickel(II) cations and chromium(VI) anions, from aqueous solutions and simulated wastewaters. The effects of pH of the solution, Ni/Cr ratio, collector and frother concentrations, induction and flotation time, and solution ionic strength on the co-removal efficiency of nickel(II) and chromium(VI) were studied. At the optimum conditions, removals more than 99.5% were obtained for nickel(II) and chromium(VI). The concerned contaminants were effectively removed when they coexisted at low as well as at high concentrations. Coflotation of nickel(II) and chromium(VI) from tap water and simulated electroplating wastewater resulted in removal percentages higher than 99.5% with residual concentrations below their permissible limits in potable water. High removal percentages, DFs, ERs, and VRs were achieved for their radionuclides, ⁶³Ni(II) and ⁵¹Cr(VI), from simulated radioactive process wastewater. The results obtained in this study suggest the feasibility of the developed foam separation process for treatment, in a single-step, of wastewaters contaminated with cationic and anionic inorganic pollutants.     

Floe Foam Flotation of Chromium(VI) with Polyelectrolytes

Abstract

The separation efficiency of the floe foam flotation of chromium(VI) with Fe(II) from aqueous solutions with high ionic strength can be improved by adding a very small amount of polyelectrolyte (either cationic or anionic polymer) as an activator. The possible mechanisms by which flotation is affected by polyelectrolytes are discussed. The effects of the order of the addition of the reagents (polyelectrolyte and base) on flotation and sedimentation are also studied. It was found that effective separation of chromium(VI) by floe foam flotation with Fe(II) can be achieved for a rather wide range of initial chromium(VI) levels by using the same treatment parameters.     

Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

In this study, bio-chars were evaluated as a potential adsorbent for the removal of Cr (VI) ions from aqueous solutions. The effects of some important parameters including initial pH (1.5–7), adsorbent dose (0.2–5 g/L), contact time (5–900 min) and initial Cr (VI) ion concentration (5–75 mg/L) were tested on the removal of Cr (VI) ions from aqueous solution in batch experiments. Maximum adsorption capacities of the tested bio-chars under the certain experimental conditions determined as optimal were 3.53 mg/g for NCBC, 3.97 mg/g for NZCBC and 6.08 mg/g for ACBC, respectively. Results of the kinetic and isotherm modeling studies revealed that the adsorption data fitted well with a pseudo-second order and Langmuir model. In among the tested bio-chars, the bio-char (ACBC) was largely equivalent to activated carbon: AC (9.97 mg/g) in terms of adsorption capacity. All results indicated that the bio-chars had higher adsorption capacity than some chars and activated carbons reported previously, and also that these bio-chars could be used successfully as low-cost adsorbents for the removal of chromium ions from aqueous solutions under the tested experimental conditions.     

Synergistic Extraction of U(VI), Th(IV), and Lanthanides(III) from Nitric Acid Solutions Using Mixtures of TODGA and Dinonylnaphthalene Sulfonic Acid

The extraction of U(VI), Th(IV), and lanthanides(III) from aqueous nitric acid solutions with mixtures of N,N,N′,N′-tetra(n-octyl)diglycolamide (TODGA) and dinonylnaphtalene sulfonic acid (HDNNS) in n-decane has been investigated. The extraction efficiency of U(VI), Th(IV), and Ln(III) ions is greatly enhanced by addition of HDNNS to an organic phase containing TODGA. The synergistic effect arises from the higher hydrophobicity of U(VI), Th(IV), and Ln(III) extracted species formed by TODGA and DNNS^? anions as compared to those formed by TODGA and NO₃^? ions as counter anions. The synergistic effect for U(VI), Th(IV), and Ln(III) extraction from aqueous nitric acid solutions with mixtures of TODGA and HDNNS becomes weaker when the acidity of the aqueous phase increases. A high synergistic enhancement is accompanied with a high selectivity of Ln(III) extraction from nitric acid solutions.     

Liquid-Liquid Phase Distribution Studies of Chromium(VI) between Mineral Acid Solutions and 5-(4-Pyridyl)nonane N-Oxide in Benzene,and Enrichment by Extraction Plant with Pulsation Column

Abstract

A liquid-liquid extraction system consisting of a benzene solution of 5-(4-pyridyl)nonane N-oxide (P_yNO_x) and mineral acid solutions has been studied for the extraction of chromium(VI). The optimal conditions for the extraction have been carefully selected from a critical study of the various factors involved, such as the effects of the concentration of the mineral acids, chromium, and the solvent; and the salting and complexing agents. Common anions have little effect on extraction in concentrations up to 0.5 M. Backextraction of the metal can be accomplished by a number of solutions and by water. Extraction of several metals was investigated under optimal conditions for the extraction of chromium. Common base metal ions like iron, aluminum, magnesium, calcium, etc. are not extracted. The mechanism of extraction has been studied by using slope analyses and saturation experiments. The predominant mode of extraction appears to be ionic association with the probable composition of the extracted species being P_yNO_xH⁺.HCr₂O₇ ^?, with some additional contribution by benzene. Extraction at a high aqueous to organic ratio has been studied by using an extraction plant with a pulsation column.     

Core–sheath nanofibrous membranes based on poly(acrylonitrile-butadiene-styrene), polyacrylonitrile,and zinc oxide nanoparticles for photoreduction of Cr(VI) ions in aqueous solutions

This investigation addresses the design of a series of poly(acrylonitrile-butadiene-styrene)/polyacrylonitrile–zinc oxide(ABS/PAN–ZnO) membranes by coaxial electrospinning. In the first instance, an optimization of ABS and PAN electrospinning was performed, thus establishing suitable compositional and processing parameters for obtaining homogenous fibers. Then, coaxial electrospinning of ABS and PAN solutions containing different amount of ZnO nanoparticles was carried out. The coaxial morphology of the nanofibers and ZnO distribution/dispersion were studied by the combination of several techniques such as scanning electron microscopy, X-ray energy dispersive analysis, contact angle, and thermogravimetric analysis. The performance of the obtained membranes for chromium (VI) ions removal from aqueous solutions was assessed by photoreduction using ultraviolet–visible spectroscopy. Electrospun mats composed of ABS (core)/PAN (sheath) embedded with 30 wt % of ZnO nanoparticles exhibited the highest chromium photoreduction (about 80%), suggesting the potential use of these membranes as filters for water purification. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48429.     

Dissolution of silicon and junction delineation in silicon by the CrO3-HF-H2O system

The dissolution of single crystal silicon by aqueous solutions of hydrofluoric acid and chromium (VI) oxide was studied as a function of the resistivity of silicon and the composition of the etchant. In the concentration range under study, the dissolution rate is dependent on the resistivity of the silicon. The dissolution process is controlled by the chemical reaction rather than by the diffusion of chemical species; the rate of the chemical reaction is limited by the supply of carriers at the silicon surface. When the etchant was 2 M in chromium (VI) oxide, the dissolution rate of silicon of a given resistivity is second order with respect to hydrogen fluoride, suggesting that the formation of bivalent silicon is probably the rate-determining step of the chemical reaction.

An aqueous solution of hydrofluoric acid and chromium (VI) oxide can be used for delineating electrical junctions and revealing certain resistivity variations in silicon. A technique for this purpose is described and applied to multilayer silicon specimens. The relative etch rates of the various layers depend on resistivity somewhat differently from isolated specimens of similar resistivities, presumably     

Synthesis of cross-linked graft copolymer from [2-(methacryloyloxy)ethyl] trimethylammonium chloride and poly(vinyl alcohol) for removing chromium(VI) from aqueous solution

A novel graft copolymer of [2-(methacryloyloxy)ethyl] trimethylammonium chloride onto poly(vinyl alcohol) has been synthesized and it is cross-linked by glutaraldehyde for the investigation of its efficiency in removing Cr(VI) from aqueous solution. The chemical nature of the ion-exchange resin has been elucidated with the help of chemical test, Fourier transform infrared, thermo gravimetric analysis and DTA. Particle size, surface area, ion-exchange capacity, optimum pH, reaction time and temperature for Cr(VI) extraction were determined. Chromium(VI) adsorption kinetics, isotherm and thermodynamics have been studied. A plausible mechanism for chromium ion-exchange has been suggested.     

Removal of chromium (VI) from aqueous solutions using poly(4‐vinyl pyridine) beads

Sorption of hexavalent chromium ions from aqueous solution by poly 4‐vinyl pyridine [Poly(4‐VP)] was studied. The batch method was applied for adsorption processes. The effects of initial ion concentration, time, pH and temperature on adsorption were investigated. A treatment time of 60 min was found to be sufficient to reach equilibrium. pH 3.0 was found as the optimum pH value for the process. The maximum adsorption performance was achieved at 86.7 mg g^?1 using 500 mg L^?1 Cr (VI) solutions. The process of adsorption of Cr (VI) was explained by Langmuir isotherm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2865–2870, 2006     

Development of Liquid Membrane Pertraction for the Removal and Recovery of Chromium from Aqueous Effluents

Abstract

Liquid membrane pertraction combines the loading and stripping steps of solvent extraction into a single unit operation, allowing the continuous removal and concentration of a given species. In this paper the feasibility of applying liquid membrane pertraction to the recovery of chromium (Cr(VI) from aqueous effluents with the objective of reducing levels to below allowable discharge limits has been examined. A continuous laboratory-scale liquid membrane pertractor was constructed to solve a variety of problems associated with the treatment of Cr(VI)-bearing streams. Various operational factors such as feed velocity, strip velocity, membrane velocity, and composition of the inlet feed were then examined. Satisfactory continuous runs lasting up to 22 days were achieved. Chromium levels in synthetic waste could be reduced from 200–300 mg/L down to 1 mg/L, well within most allowable discharge limits. Experiments showed that the strip phase can be concentrated with inlet Cr(VI) concentrations of 2000 ppm Cr(VI), with indications that it should be possible at even higher concentrations.     

Liquid-Liquid Extraction of Uranium(VI) from Aqueous Solution using 1-Hydroxyalkylidene-1,1-diphosphonic Acids

The extraction of uranium(VI) from aqueous solutions has been investigated using 1-hydroxyhexadecylidene-1,1-diphosphonic acid (HHDPA) and 1-hydroxydodecylidene-1, 1-diphosphonic acid (HDDPA), which were synthesized and characterized by elemental analysis and by FT-IR, ¹H NMR, ³¹P NMR spectroscopy. In this article, we propose a tentative assignment for the shifts of those two ligands and their specific complexes with uranium(VI). We carried out the extraction of uranium(VI) by HHDPA and HDDPA from [carbon tetrachloride?+?2-octanol (v/v: 90%/10%)] solutions. Various factors such as contact time, pH, organic/aqueous phase ratio, and extractant concentration were considered. The optimum conditions obtained were: contact time?=?20 min, organic/aqueous phase ratio?=?1, pH value?=?3.0, and extractant concentration?=?0.3 M. The extraction yields are more significant in the case of the HHDPA which is equipped with a hydrocarbon chain, longer than that of the HDDPA. Logarithmic plots of the uranium(VI) distribution ratio vs. pH_eq and the extractant concentration showed that the ratio of extractant to extracted uranium(VI) (ligand/metal) is 2:1. The formula of the complex of uranium(VI) with the HHDPA and the DHDPA is UO₂(H₃L)₂ (HHDPA and DHDPA are denoted as H₄L). A spectroscopic analysis showed that coordination of uranium(VI) takes place via oxygen atoms.